This invention relates to a method for refining wax esters by contacting them with an adsorbent capable of selectively removing trace contaminants. Jojoba oil is a commercially important wax ester which can be treated by this method. More specifically, it has been found that amorphous silicas of suitable porosity are quite effective in adsorbing phospholipids and associated metal-containing species from wax esters, to produce products with substantially lowered concentrations of these trace contaminants.
Jojoba oil is an odorless fatty alcohol ester, light gold in color. It consists of practically 100% linear wax esters, about 87% of which are combinations of straight-chain acids and alcohols. Jojoba oil is not derived from glycerol and is not a glyceride oil as are most plant seed oils. Jojoba is used primarily as an emollient in certain cosmetics, such as skin care preparations. Jojoba also is used as an additive for high-temperature or high-pressure lubricants, as well as an antifoam agent. The oil may be useful in some edible oil markets such as for cooking and salad oils.
Jojoba oil is produced from an evergreen desert shrub, with the oil obtained from the seeds of the plant by mechanical expression or solvent extraction techniques, or both. Extraction with hexane is typical. The expressed or extracted product is then ready for the bleaching operation which removes phospholipids, trace metals and color pigments. Bleaching earths have been used historically for this operaiton. Most commonly, acid-activated clay has been used in the bleaching step.
For most applications, the phosphorus content of jojoba oil must be reduced to prevent cloudiness. Phosphorus, present as phospholipids, tends to impart off colors, odors and flavors to the finish oil product and is therefore removed. Metal-containing species associated with phospholipids (i.e., iron, copper, calcium and magnesium) also are removed since they tend to promote oxidation. Clay adsorbents have been used for removal of phospholipids and trace metals, but their use results in removal of natural antioxidants as well and the treated jojoba oil tends to lose its naturally excellent oxidative stability. Moreover, significant quantities of oil are lost in clay filter cakes. In processing jojoba oil, which is a relatively expensive oil, these losses are quite costly.
Amorphous silicas previously have been used in the purification of glyceride oils. For example, U.S. Pat. No. 4,629,588 (Welsh et al.) discloses the use of amorphous silica adsorbents for the removal of phospholipids and associated metal ions from glyceride oils. Glyceride oils, typically vegetable oils, are comprised of esters of glycerol and fatty acids in which one, two or three hydroxyl groups of the glycerol have been replaced by acid radicals.
As disclosed herein, it now has been found that amorphous silicas are effective in the refining of wax esters such as jojoba oil. The process described here efficiently and satisfactorily removes phospholipids and metal ions from the wax ester jojoba oil, and also reduces chlorophyll A levels. Amorphous silica alone has not been demonstrated to be effective for removal of chlorophyll A from glyceride oils.